I. Field of the Invention
The present invention relates to method and apparatus for assuring the proper seating of beads of tubeless tires upon their wheel rims in a production line setting.
II. Description of the Prior Art
In present-day tire-wheel assembly lines, at a point on the line just prior to the tire mounting apparatus, a tubeless tire is positioned upon a horizontally disposed wheel with a relatively small circumferential portion of the beads positioned between the opposed rims of the wheel and the remainder of the tire inclined upwardly and rearwardly in a slanted position upon the wheel. The tire and wheel are then advanced to the mounter, and during passage through the mounter a horizontally disposed roller forces the beads downwardly past the uppermost rim of the wheel. See, for example, U.S. Pat. No. 4,621,671. Because the diameter of the central opening of the tire (the inner diameter of the bead) is smaller than the diameter of the wheel rim over which it must be forced, the beads are subjected to substantial stretching and twisting forces as they are forced past the wheel rim. In an attempt to facilitate the forcing of the tire over the rim, it is standard practice to apply a lubricant or soap to the wheel rim just prior to initially positioning the tire upon the wheel. This soap is chosen to have a relatively short period of effectiveness as a lubricant to minimize the possibility of slippage of the tire rotatively relative to its wheel after the assembled tire and wheel have been balanced and mounted upon a vehicle.
In the case of lighter weight, standard-sized tires, the side walls of these tires possess sufficient flexibility so that once mounted upon the wheel, prior to inflation the tires fit loosely within the wheel rim; and when the wheel and tire are in a horizontal position, the upper bead may even droop downwardly out of contact with the upper wheel rim. In the heavier tires, particularly the low-profile, wide-tread tires used on high-performance vehicles, the tire side walls are extremely stiff, and even when uninflated the mounted tire will have its beads tightly pressed against both of the opposed rims of its wheel. Experience has shown that the twisting and rolling forces exerted on the tire bead as it is forced around the rim in the mounting operation will frequently cause the beads of these high-performance tires to be mechanically wedged or trapped in a cocked or twisted position relative to the bead engaging seat on the wheel rim. The stiffness and designed tight fit of these heavier tires will frequently preserve this flawed seating through the conclusion of the inflation operation. In those cases where inflation does not result in the elimination of the flawed seating, the flaw may in effect be locked into place by the internal pressure within the tire.
While such seating flaws may, on occasion, occur with the lighter-weight, standard tires, the lighter-weight tires possess sufficient flexibility so that the flaw will usually work itself out after a few miles on the road. This self-correcting action or driving out of the flaw very seldom occurs in the case of the relatively stiff, low-profile, wide-tread tires. The flaw typically occurs near the inner circumference of the bead and it is not possible to detect the presence of the flaw by visual inspection. The existence of the flaw may manifest itself by vibrations at various critical road speeds; but typically by the time the flaw has been detected, the tire bead has been damaged to a point requiring replacement of the tire.
The prior art has recognized that problems exist in seating the beads of tubeless tires upon their wheel rims. However, most of the efforts in the prior art have been directed to apparatus operable to engage both tire beads with the wheel rim so that the tire can be inflated through the valve stem mounted on the wheel. See, for example, U.S. Pat. Nos. 3,422,875 and 3,973,615 and the prior art cited in those patents. While these last prior art devices are useful in service stations for mounting replacement tires, they are not designed to correct a flawed bead seating after a tire has been inflated to design pressure, nor are they practical for use in a production line environment which may be required to operate at line speeds of up to 400 units per hour. At these line speeds, it is not practical to attempt to inflate the tires via the wheel valve stem--the tire is inflated by means of a head which forces air under pressure into the tire between the wheel rim and one bead of the tire. See, for example, U.S. Pat. No. 4,183,392.
The prior art has also approached this problem with so-called dynamic run-in machines. In these machines, a mounted and inflated tire-wheel unit is positioned with the wheel unit axis vertical between three tread-engaging rollers mounted for rotation about vertical axes. The rollers are pressed radially inwardly against the tire tread, and one roller is driven in rotation to likewise drive the tire and wheel unit in rotation while the rollers press radially inwardly against its tread. This is intended to correct flawed bead seating by an in-plant simulation of road conditions which, as described above, will correct flawed bead seating in the lighter-weight, standard-sized tires. However, as stated above, correction by this method cannot always be accomplished in the case of low-profile, wide-tread tires. Further, the prior art dynamic run-in machines were found to be expensive to make, operate and maintain and presented a substantial safety hazard in that the rapidly rotating wheel unit was held only by the frictional grip of the tread-engaging rollers.
Another method was to inflate the tire to an extremely high pressure (e.g. 65 psl) and then bleed the pressure back through the valve stem to design pressure. This particular process was too slow and cumbersome to be practical on a production line.
The present invention is especially directed to a method and apparatus for correcting flawed bead seating which may be used upon an inflated tire-wheel unit while stationary on a tire-wheel assembly line operating at a high-production rate.